Safe vessel berthing is always an emphatically studied object in the water transportation field. In the process of berthing a vessel at a port or a wharf, the berthing speed and distance needs to be controlled strictly, and the attitude of the vessel also needs to be considered. A pilot must know very well geographic features, waterways, depth of water, water flow, settings of navigation marks, and local rules and regulations within a water area, and must have proficient skills for handling high berthing difficulties. Therefore, the pilot has very high working intensity, and also faces various safety risks.
In the water transportation field, severe weather, particularly foggy weather, seriously affects the smoothness of waterways. Statistical maritime data indicated that most of maritime accidents occur at night or in restricted visibility, and the maritime accidents in restricted visibility were in the majority; and fog is one of the most important factors causing the restricted visibility. When a vessel navigates in fog, due to various uncertain factors (e.g., the dynamic state of the vessel, the subjective intention of a navigator or the like), the navigator often makes a wrong decision, resulting in a maritime accident. At present, devices for aiding navigation mainly include a radar navigation system and an automatic identification system.
As for vessel piloting, the foggy weather will seriously influence the visual observation effect of a pilot, and consequently, the pilot is unable to judge the attitude of a vessel relative to a berth and thus unable to conduct the safe berthing of the vessel. Even if hydrological conditions at different ports and waterways are different, vessels will generally slow down at a visibility less than 1 sea mile, and large vessels will generally stop at a visibility less than 1000 m. Due to low visibility in the foggy weather, serious accidents often occur, for example, large vessels crash into piers. Meanwhile, vessel's passing a dam is influenced by the foggy weather, and the vessel must stopping passing the dam in the foggy weather. Therefore, the foggy weather not only influences the safety of vessel navigation, and also seriously influences the smoothness of waterways and port logistics.
At present, during the navigation and berthing of a vessel, some radio piloting systems, for example, radar, will be used for reference. However, a radar system is easily affected by external factors, such as weather, topography and external disturbance. Moreover, since the radar is generally erected at a high position on a vessel, it is difficult to detect conditions at a close distance from the vessel although it can detect conditions at a large distance from the vessel. Therefore, the radar system has great limitations during the piloting and berthing of a vessel. At present, a vessel berthing scheme is generally determined based on the visual estimation and judgment of a pilot. To avoid the occurrence of potential accidents, it is stipulated that no vessel's navigation and transportation is allowed in the severe weather.
Considering the actual demands of huge freight volume and turnover volume of passenger traffic nowadays, some navigation aids used in the severe weather have been developed, for example, a radar navigation system, an Automatic Identification System (AIS) and the like in the navigation field. Although these navigation aids may assist a navigator in navigating in the severe weather conditions, they still have many disadvantages due to many aspects such as technology, cost, precision and site.
Both the radar navigation system and the AIS in the prior art are navigation aid systems based on radio communication. As the common means for vessel navigation assistance, a radar navigation system for vessels has inevitable defects although it works well in positioning, navigation and collision prevention. For example, in the severe weather conditions (e.g., rainy, snowy or stormy weather), the radar navigation system is easily interfered by sea waves, rain and snow to generate clutters; and radars at a same frequency or an approximate frequency will also generate co-frequency radar interference clutters at a close distance. Moreover, the radar generally has a fixed blind zone of 30 m to 50 m, so that a sectored shadow zone will be generated due to the influence from objects such as a mast on the vessel. Additionally, due to the influence from complicated conditions, the radar will generate various false echoes, for example, multi-trace false echo, second-trace false echo, indirect-reflection false echo, side-lobe echo and the like. In the actual use, all the interference clutters and the false echoes will often make a manipulator difficult to distinguish or observe, and thus result in wrong guidance for navigation.
The Automatic Identification System (AIS) for vessels is a device based on satellite positioning, with a precision of 5 m to 30 m. Due to the absence of any blind zone, its positioning precision is higher than that of the radar and does not change with the change in distance and orientation of a target. The AIS consists of shore-based (base station) facilities and ship-borne devices, and is a novel digital navigation aiding system and device integrating the network technology, the modern communications technology, the computer technology and the electronic information display technology. The AIS is essentially a broadcast transponder system which operates on a maritime mobile communication channel VHF and can automatically transmit information about a vessel (e.g., the name of the vessel, call sign, maritime mobile service identity, location, course, speed and the like) to other vessels or the shore, process multiplex communication at a rapid update rate, and use a self-control time division multiple access technology to fulfill the high density of communication, so that the reliability and real-time performance of ship-to-ship and ship-to-shore operations are ensured. However, the AIS still has many limitations. Firstly, like the radar navigation system, the provided information is not a real visual image and thus does not really help the berthing and navigation in the foggy weather. Since a pilot fails to see the ambient environment, the vessel also needs to be stopped. Secondly, the equipment precision of 5 m to 30 m perhaps meets the requirements for collision prevention; however, for close-distance berthing, a precision error of 5 m easily results in a serious collision of a large vessel with a wharf or a lighter at the critical moment of berthing.
In conclusion, the two navigation aids in the prior art, i.e., the marine radar navigation system and the ship-borne AIS, still cannot make a vessel berthed safely during close-distance navigation in the low-visibility conditions.
Recently, solar blind ultraviolet navigation and berthing systems have been developed in the prior art. On the basis of the solar blind ultraviolet phenomenon within a waveband of 200 nm to 280 nm, a group of solar blind ultraviolet light source lamps are provided on the shore, and a solar blind ultraviolet detector is provided on a vessel to be navigated and berthed. The position of the vessel relative to a wharf is eventually obtained according to the solar blind ultraviolet signals received by the detector, so that it is advantageous for safe berthing. For example, Chinese Patent Application No. 2012105507102, entitled NAVIGATION AND BERTHING SYSTEM BASED ON SOLAR ULTRAVIOLET SIGNALS, has disclosed a solar blind ultraviolet auxiliary berthing system. The system consists of a solar blind ultraviolet light source system, a three-axis electronic compass, an optical imaging module and an information processing terminal. The three-axis electronic compass is connected to the optical imaging module to acquire angular information of the optical imaging module during rotation. The optical imaging module includes a spectroscope, a visible or infrared imaging channel and a solar blind ultraviolet imaging channel, wherein the visible or infrared imaging channel receives visible light signals and outputs visible or infrared video signals, and the solar blind ultraviolet imaging channel receives solar blind ultraviolet signals and outputs solar blind ultraviolet video signals. The information processing terminal is used for calculating navigation attitude data of the vessel according to digital signals of the two videos and then outputting a composite video to a display system. In this patent application, by connecting the three-axis electronic compass to the optical imaging module, the angular information of the optical imaging module during rotation is acquired, and angular information of the vessel relative to the shoreline is eventually obtained. However, this system still has some disadvantages. For example, when in use, the three-axis electronic compass will be interfered by a large magnetic field sometimes, so that the obtained data has an error. As a result, it is very difficult to obtain the accurate distance from the vessel to the shoreline of a berth, and it is thus difficult to realize safe berthing.
Therefore, in the prior art, the accurate positioning, berthing and piloting of a vessel in the foggy weather cannot be ensured conveniently, accurately and safely at present.